Every single day.
And I've spent a lot of time supply teaching. The curriculum for most, if not all, subjects is aimed at white males and written by white males. I've done a lot of supply so seen a lot of subjects.
The school uniforms arw based on 1950s grammar school uniform, the food in most schools / colleges is typical of that cooked in a white Brisish home. You might get the odd curry.
The text books, they might show people of different colours but when you get to the section on nutriton there will be pictures of chips but not samosas or akee.
I had a class writing their CVS, they listed all their GCSE grades but not their languages, when I asked them why they didn't put the language down they said because they didn't have a GCSE in it.
Some of the students were fluent in 3 languages, but they had not had hte oportunity to study those languages.
There is an idea in linguistics that anguages have a 'value' or 'prestige', someone fluent in English, Spanish and French is considered clever, someone fluent in English, Urdu and Punjabi isn't.
Language departments in school almost all centre on European languages. Now I know that for many people they will not travel outside Europe and in terms of 'value' Spanish has millions of users but there is no reason why schools can't add in other languages, particularly in an area where there are a lot of children whose parents / grandparents are native speakers.
Even the local Sikh school, which does teach Punjabi, doesn't make it a compulsory subject for non Sikh children.
Sorry slight rant there.
In my pewerpoints I try to include things left out of the text books so if I'm teaching about making a snack, then I'll have a slide with various types of tea, with cardamon made in a pan, made in a tea pot with leaves, in an urn served in glasses. It's a tiny thing that takes no time at all.